Device for heating a liquid, and deep-frying vessel with such a device

ABSTRACT

Device for heating a liquid in a holder, comprising a heater element ( 31 ) designed to be placed in said holder and to be immersed in liquid in said holder, a temperature sensor ( 65 ) for measuring the temperature of the liquid in the holder and coupled to a control unit ( 41 ) for the thermostatic control of power supply to the heater element ( 31 ), a thermal safety cut-out ( 60 ) for interrupting the power supply to the heater element in response to heating-up of the heater element to above a given temperature, which safety cut-out ( 60 ) is in thermally conductive contact with the heater element ( 31 ), and a carrier ( 50 ) which is thermally coupled by means of a thermal coupling to a portion of said heater element which is immersed in the liquid in said holder in the operational state, the temperature sensor ( 65 ) of the thermostat being situated on said carrier ( 50 ) at a distance from said thermal coupling.

[0001] The invention relates to a device for heating a liquid in aholder, comprising:

[0002] a) a heater element designed for placement in said holder and forimmersion in said liquid,

[0003] b) a temperature sensor for measuring the temperature of liquidin the holder and coupled to a control unit for the thermostatic controlof power supply to the heater element,

[0004] c) a thermal cut-out arranged for interrupting the power supplyto the heater element in response to heating of the heater element toabove a given temperature, which cut-out is in thermally conductivecontact with the heater element, and

[0005] d) a carrier which is thermally coupled via a thermal coupling toa portion of said heater element, which element is immersed in liquid insaid holder in the operational state.

[0006] Such a device is known from German utility model DE-U-6944402.Such heating devices are used, for example, for heating fat indeep-frying pans, but they may alternatively be used for heating otherliquids, such as water in a water kettle. The current supply to theheater element is thermostatically controlled in dependence on thesensed temperature of the fat, the temperature sensor of thethermostatic control being present in the fat separated from the heaterelement. If there is an insufficient quantity of fat in the holder, orif the thermostatic control is defective, it could happen that thecurrent supply to the heater element is not switched off and the heaterelement or the fat present becomes too hot. The latter may even lead toignition of the fat.

[0007] As a safeguard against such undesirable effects, according to thecited German utility model, a heat protection switch is accommodated ina housing which is in contact with the heater element. This heatprotection switch forms a thermal safeguard which prevents overheatingof the heater element in the situation described above. The housing inthis case extends through the bottom of the holder for containing thefat and forms a support for the heater element adjacent a free endthereof.

[0008] A disadvantage of this is that the deep-frying vessel, and inparticular the heating device thereof, is of a comparatively complicatedconstruction and is accordingly comparatively vulnerable and expensive.

[0009] It is an object of the invention to provide a heater element forheating liquid in a holder which is of a simpler construction, whileretaining a thermostatic temperature control and a thermal protection ofthe heater element.

[0010] A device according to the invention is for this purposecharacterized in that the temperature sensor of the thermostat issituated at a distance from said thermal coupling on said carrier.

[0011] Since the temperature sensor and the thermal cut-out are providedin a common housing, a single housing suffices for the accommodation ofthe temperature sensor and the thermal cut-out. Since the temperaturesensor of the thermostatic control is located at a distance from thethermal coupling of the housing to the heater element, said sensor willstill assume primarily the temperature of the liquid in the holderduring operation. The temperature of the temperature sensor is thusinfluenced by the temperature of the heater element to a minor degreeonly. This latter temperature indeed stays within a comparatively narrowtemperature range during normal operation.

[0012] Particularly advantageous embodiments of the invention aredefined in the dependent claims.

[0013] The invention may be advantageously used in a deep-fryingapparatus whose holder and heating device are designed so as to match toone another.

[0014] Further aspects, effects, and constructional details of theinvention will now be explained in more detail with reference to anembodiment and the drawings, in which:

[0015]FIG. 1 is a diagrammatic cross-sectional view of an embodiment ofa deep-frying apparatus and a device according to the invention, and

[0016]FIG. 2 is a side elevation of part of the device of FIG. 1.

[0017] The embodiment shown in FIG. 1 relates to a deep-frying apparatus1 and a heating device 20 thereof.

[0018] The deep-frying apparatus 1 comprises a pan 10 as the holder, inwhich a quantity of deep-frying oil or fat is present up to a level 11′in the pan 10 in the operational state as shown. The heating unit 20 isremovable and is substantially composed of a heating part 30 and ahandle 40 in which a control unit 41 for controlling the current supplyto the heating unit 30 is accommodated.

[0019] The heating part 30 can be taken from the pan 10 or placed in thepan 10 by means of the handle 40. The pan 10 can thus be easily andfully separated from the electrical heating unit 20. This renderscleaning of the pan 10 easy; it can even be done in a dishwasher.

[0020] The heating part 30 is provided with a tubular electric heaterelement 31 (see also FIG. 2) whose two tubular portions 32 extend inhorizontal direction from the handle 40 and merge into vertical portions33, in the operational position shown, and then again into horizontalportions 34 which extend adjacent the bottom 10′ of the pan 10 in theoperational state. The tubular heater element follows a meanderinglooped path in the region 34. The heater element 31 is connected to thecontrol unit 41 accommodated in the handle 40, by means of which unitthe heater element 31 can be switched on and off. Such heater elementsare known from practice and convert an electric current into heat.

[0021] A carrier 50 extends alongside the heater element 31, supportinga thermal cut-out 60 and a temperature sensor 65. In this example, thecarrier is constructed as a tubular housing 50 in which the thermalcut-out 60 and the temperature sensor 65 are accommodated. The tubularhousing 50 has a fixed end 51 which is connected to the handle 40 andwhich is substantially parallel to the horizontal portion 32 of theheater element 31. At a distance from the handle 40 and adjacent thevertical portions 33 of the heater element 31, the tubular housing 50merges into a portion which extends vertically downward, parallel to thevertical portion 33 of the heater element 31. Since the tubular housing50 runs parallel to the heater element 31 for a major portion, thetubular housing 50 is at least partly screened off by the heater element31, so that the tubular housing 50 is protected against impacts.Furthermore, an immersion heater of a slim overall shape is obtainedthereby, which occupies little space in the pan and accordingly leavesmuch space for food to be deep-fried.

[0022] At a distance from the portions 32 of the heater element 31,which are substantially horizontal during use and which merge into thehandle 40, the tubular housing 50 is thermally coupled to a portion 33of the heater element 31 which lies below the level 11′ of the fat 11 inthe pan 10 during operation, provided enough fat is present by means ofa thermally conducting connecting portion 53.

[0023] The end 54 lying in bottom position during use of the housing 50lies approximately at the level of the horizontal portion 34 of theheater element 31. In the example shown, the end 54 of the tubularhousing 50 is slightly below the plane of the horizontal portion 34. Theend 54 of the tubular housing 50 is closed off so as to be impermeableto liquid in this example. As a result, the thermal cut-out 60 and thetemperature sensor 65 do not come into direct contact with the liquidfat in the pan. This means that the thermal cut-out 60 and thetemperature sensor 65 need not be resistant to heated liquids like fator water, as applicable, and use may be made of, for example,inexpensive electronic temperature sensors. The tubular housing 50 inthis example has a circular cross-section. A cross-section ofalternative shape, however, is also possible, a cross-section differingfrom the circular offering the advantage of an enlarged contact surfacearea with the fat, whereby a more intensive heat transfer between thefat and the housing 50 is obtained. The housing may indeed be other thantubular in shape, but the tubular design offers the advantage thatmanufacture is simple and the hermetic closure of the housing issafeguarded, while at the same time a guiding and screening of theconductors of the circuits of the sensors in the housing is obtained ina simple manner in the tubular design. Preferably, the housing 50 ismanufactured from a thermally conducting material such as, for example,aluminum.

[0024] The thermal cut-out 60 is provided in the tubular housing 50 atthe level of the connecting portion 53 in the form of a circuit breakerwhich is capable of interrupting a circuit in which it is connected uponreaching a given maximum admissible temperature. The thermal cut-out 60is connected with heat conduction to the tubular housing 50, such thatheat from the heater element 31 can be transferred to the thermalcut-out 60 via the connecting portion 53 and the wall of the tubularhousing 50. The thermal cut-out 60 is connected to the control 41 bymeans of an electrical wiring 61 which is passed through the tubularhousing 50. In the operational state, both the housing and the thermalcut-out are in thermally conductive contact with the oil to be heated,so that the cut-out and the housing are cooled by the oil. The thermalcut out accordingly responds quickly to an insufficient oil level in thepan owing to the disappearance of the cooling effect of the oil. Anelectrical temperature sensor 65 is accommodated in the tubular housing50 at a distance from the thermal cut-out 60. The sensor 65 is includedin a circuit with wiring 66 extending through the tubular housing 50 andconnected to the thermostatic control unit 41. The temperature sensor 65is in thermally conductive contact with the tubular housing 50 so thatthe sensor 65 assumes the temperature of the fat present in the pan 10.The wiring 61, 66 is entirely surrounded by the tubular housing 50 fromthe relevant sensor up to the handle, so that the wiring is wellprotected against damage during use.

[0025] During operation, a quantity of fat or oil 11 is introduced intothe pan 10, for example up to a level 11′, whereupon the heating unit 20is put on the edge of the pan 10 and clamped thereon. The horizontalportion 34 of the heater element 31 will then lie below the level 11′ ofthe fat 11. The end 54 of the tubular housing 50 is accordingly alsoimmersed in the fat. Then current is supplied to the heater element 31under the control of the control unit 41, so that the heater element 31becomes hot and the fat 11 is heated.

[0026] During heating, the control 41 detects the measuring signalscoming from the temperature sensor 65 and controls the current supply tothe heater element 31 in dependence on the signals received and apossibly preset temperature. In addition, the temperature sensed by thethermal cut-out 60 is detected. Since the thermal cut-out 60 is inthermal contact with the heater element 31, the cut-out primarilyassumes the temperature of the heater element 31. The temperature sensor65, which is indeed situated in the same housing 50 as the thermalcut-out, but at a distance from the latter, in its turn primarilyassumes the temperature of the fat 11. For this reason it isadvantageous that it is situated approximately at a level with orslightly higher than the heater element 31. It is furthermoreadvantageous for the heat transfer from the fat to the temperaturesensor 65 that the latter lies at the end of the housing 50 where it ismore surrounded by the fat whose temperature is to be measured, and notat a distance from the end 54 of the tubular housing 50.

[0027] If the temperature detected by the thermal cut-out becomes toohigh, for example owing to an insufficient quantity of fat in the pan ora defect of the heater element 31 or the temperature sensor 65, thecontrol 41 switches off the heater element 31. A safe operation of theheating device is safeguarded thereby.

[0028] The temperature sensor 65 and the thermal cut-out 60 are wellprotected against damage, for example owing to impacts, in that they aresituated in the hollow tubular housing 50. The fact that the sensors arescreened off from the fat means that it is also possible to usecomparatively simple sensors. In particular, according to the invention,inexpensive electronic temperature sensors may be used.

1. A device for heating a liquid in a holder (10), comprising: a) aheater element (31) designed for placement in said holder and forimmersion in said liquid, b) a temperature sensor (65) arranged formeasuring the temperature of liquid in the holder and coupled to acontrol unit (41) for the thermostatic control of power supply to theheater element (31), c) a thermal cut-out (60) for interrupting thepower supply to the heater element in response to heating of the heaterelement to above a given temperature, which cut-out (60) is in thermallyconductive contact with the heater element (31), and d) a carrier (50)which is thermally coupled via a thermal coupling to a portion of saidheater element, which element is immersed in liquid in said holder inthe operational state, characterized in that the temperature sensor (65)is situated at a distance from said thermal coupling on said carrier(50).
 2. A device as claimed in claim 1, wherein the carrier (50) isformed by a housing which is impermeable to liquids in the operationalstate when immersed at least partly in liquid, and wherein thetemperature sensor and the thermal cut-out are arranged inside thehousing (50).
 3. A device as claimed in claim 2, wherein the housing(50) is tubular, and the temperature sensor (65) and the thermal cut-out(60) are situated at a distance from one another in longitudinaldirection of the tubular housing.
 4. A device as claimed in claim 2 or3, wherein the housing (50) and the heater element (31) are constructedas an immersion heater with a portion which is substantially vertical inthe operational state and which is designed for extending from an edgeregion of the housing down into the liquid.
 5. A device as claimed inclaim 4, wherein conductors of circuits of which the temperature sensor(65) and the thermal cut-out (60) form part are passed through thehousing (50) to the control unit (41).
 6. A device as claimed in claim 4or 5, wherein the heater element (31) has a portion (34) which extendsmainly in horizontal direction and a portion (33) which extends mainlyin vertical direction, the housing (50) extending substantiallyalongside said vertical portion (33).
 7. A device as claimed in any oneof the preceding claims, wherein the temperature sensor (65) is situatedin an end of the carrier (50).
 8. A device as claimed in any one of thepreceding claims, wherein said thermal coupling between the carrier (50)and the heater element (31) is situated adjacent the thermal cut-out(60).
 9. A device as claimed in one of the claims 2 to 8, wherein thetemperature sensor (65) is constructed as an electronic temperaturesensor.
 10. A deep-frying apparatus provided with a device as claimed inany one of the preceding claims and with a holder (10) for accommodatinga liquid to be heated.
 11. A deep-frying apparatus as claimed in claim10, wherein said device in the operational state extends from an edgeregion of said holder to adjacent a bottom (10′) of said holder (10).